Crystalline polystyrene products

ABSTRACT

HIGHLY CRYSTALLINE, ISOTACTIC POLYSTYRENE PRODUCTS HAVING MOLECULAR WEIGHT OF LESS THAN 1,000,000 ARE PREPARED BY THE THERMAL DEGRADATION IN AIR AT TEMPERATURES BETWEEN 100*C. AND 260*C. OF HIGH MOLECULAR WEIGHT, HIGHLY CRYSTALLINE COPOLYMERS OF STYRENE WITH 2-20 PERCENT BY WEIGHT OF AN ALPHA-OLEFIN HAVING 3 TO 10 CARBON ATOMS. THE INITIAL COPOLYMERS HAVE A MOLECULAR WEIGHT IN EXCESS OF 1,000,000. THE RATE OF DEGRADATION OF THE COPOLYMERS OF THIS INVENTION IS GREATER THAN THE RATE OF DEGRADATION OF POLYSTYRENE AT THE SAME TEMPERATURES. THE CRYSTALLINITY OF THE RESULTING POLYSTYRENE PRODUCT IS GENERALLY HIGHER THAN THAT OF THE INITIAL COPOLYMERS.

GC. 24, 1972 G E HULSE ETAL CRYSTALLINE POLYSTYRENE FRGDUCTS Filed Dec.22, 1971 N @Dx O5 CD1] /W )msoosm amlvlaa U.S. Cl. 260-88.2 C 4 ClaimsABSTRACT F THE DISCLOSURE Highly crystalline, isotactic polystyreneproducts having molecular weight of less than 1,000,000 are prepared bythe thermal degradation in air at temperatures between 100 C. and 260 C.of high molecular Weight, highly crystalline copolymers' of styrene with2-20 percent by weight of an alpha-olefin having 3 to 10 carbon atoms.The initial copolymers have a molecular weight in excess of 1,000,000.'Ihe rate of degradation of the copolymers of this invention is greaterthan the rate of degradation of polystyrene at the same temperatures.The crystallinity of the resulting polystyrene product is generallyhigher than that of the initial copolymers.

BACKGROUND OF THE INVENTION This invention relates to a process for thepreparation of highly crystalline, isotactic polystyrene products havinga molecular weight of less than 1,000,000 which comprises degrading byheating in air of highly crystalline copolymers of styrene having from 2to 20 percent by weight of an alpha-olen having from 3 to 10 carbonatoms.

Isotactic polystyrenes prepared by the Ziegler-Natta catalyst system areusually polymers of very high molecular weight (in the millions) and ahigh degree of crystallinity, and as such are difficult to process byusual molding techniques. To overcome the difficulties of processing,the obvious solution is to degrade the high molecular weight,crystalline polymers to polymers of lower molecular weight (less than1,000,000). Thermal decomposition in the presence of bromine-containingcompounds has been suggested to accomplish the desired degradation.Thermal degradation in the presence of antioxidants has also beenproposed.

SUMMARY OF THE INVENTION It has now been found that highly crystallinepolystyrene products of molecular weight between 10,000 and 1,000,000can be prepared by rst preparing highly crystalline, high molecularweight copolymers of styrene containing 2 to 20 percent by weight of analpha-olefin having from 3 to 10 carbon atoms, and then heating thecopolymer in air at a temperature of between 100 C. and 260 C., wherebythe copolymer is degraded to polystyrene products having the same orgreater degree of crystallinity than the starting copolymers.

These alpha-oleins may be copolymerized with styrene to high molecularweight, crystalline copolymers with the aid of any of the Ziegler-Nattatype catalyst systems that are useful for the preparation of isotacticpolystyrene.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the relativereduction in viscosity versus time of heating at 150 C. of copolymers ofstyrene containing varying amounts of l-octene.

FIG. 2 is a graph showing the relative reduction in viscosity versustime of heating at 150 C. of copolymers of styrene containing variousalpha-olens.

DETAILED DESCRIPTION OF THE yINVENTION The copolymers of the inventionmay be made by copolymerizing styrene with suitable alpha-olens havingUnited States Patent O 3,700,639 Patented Oct. 24, 1972 ice from 3 to 10carbon atoms. Suitable alpha-olens are propylene, 1-butene, l-pentene,3methyl1butene, 1-hexene, l-octene, 1-decene, and the like.

The alpha-olefin comonomer should be present to the extent of between 2and 20 percent by weight of total copolymer. Amounts less than 2 percentgives copolymers whose rate of degradation is not appreciably greaterthan that of polystyrene. As the amount of comonomers gets greater than20 percent, the copolymers seem to approach a maximum rate ofdegradation and the increase in cost of the copolymer olfsets anyadvantage in rate of degradation.

The method of copolymerization is not critical, but the preferred methodis to utilize any of the known Ziegler- Natta type catalyst systemswhereby highly crystalline, isotactic styrene-alpha-olefn copolymers ofhigh molecular weight are obtained. Thus, a complex catalyst consistingof triisobutyl aluminum with titanium trichloride in heptane at C. givesa polymer of styrene having a molecular weight of about 2,000,000 with acrystallinity of about 26 percent and is suitable for preparing thestyrene-alpha-olen copolymers of the present invention.

The method of heating the copolymers to effect the degradation may beany of several known methods. For example, molding samples ofpolystyrene containing 4.1 percent propylene in air for 10 minutes at240 C. followed by annealing at 180 C. for 1 hour causes a drop inmolecular weight from 3,000,000 to 470,000. Where the recovery of thesample in the same physical form that one starts with it unimportant,heating may be effected in an extrusion or milling process. Thus, thesame styrenepropylene copolymers, after mastication in a BrabenderPlasticorder at 200 C. in air had a molecular weight of 105,000 after 15minutes and of only 72,000 after 30 minutes. A preferred method ofheating the copolymers is to place the copolymers in an open dish in arecirculating air oven set at the desired temperature. Temperatures ofbetween and 260 C. may be used, but the preerred temperature range isfrom to 200 C. Temperatures below 100 C. necessitate an excessively longdegradation time, whereas at temperatures above 240 C. (the meltingpoint of isotactic polystyrene), While degradation occurs, the polymericmass fuses and presents handling difiiculties.

The time of heating may be varied from 1 to 24 hours, depending on thefinal molecular weight desired and the particular copolymer involved.The initial rate of degradation increases with increasing amounts of aparticular comonomer in the copolymer as shown in the drawings at FIG.l. The initial rate of degradation also depends on the particularalpha-olefin which is copolymerized with the styrene as shown by thedrawings at FILG. 2, and the Table III. The rate of degradation alsoincreases greatly with temperature of heating as indicated by the datain Tables ll and III. The particular time and temperature required toproduce a polystyrene of a desired molecular weight can be readilydetermined by a skilled technician from a knowledge of the compositionand molecular weight of the initial copolymer and a few experiments ofthe type shown in Example II.

The degradation of the crystalline copolymers of the present inventiondoes not cause any loss of crystallinity. In most cases, thecrystallinity has been increased by the heating process. yIt is notknown whether the increase in crystallinity is due solely to annealingeiects or to the molecular weight breakdown giving smaller moleculeswhich are beter able -to crystallize. For example, a styrene-propylenecopolymer having 5.0 percent propylene, initial molecular weight of2,000,000 and an initial crystallinity of 26.25 percent was degraded byheating in air for 6 hours at 200 C. to form a polystyrene product ofmolecular weight of 24,000 and a nal crystallinity of 39.5 percent.Similarly, a copolymer of styrene with 5.7 percent l-octene having aninitial molecular weight of 4,500,000 and a crystallinity of 18.3percent was degraded for 24 hours at 150 C. to give a product ofmolecular weight 290,000 and a crystallinity of 34.1 percent. Allcrystallinities were measured by differential scanning calorimetry.

Molecular weights of the various polystyrene products were calculatedfrom the intrinsic viscosity in chlorobenzene at 30 C. on the basis ofthe formula [11] =KMa where [11] :intrinsic viscosity in 100 cc./ g.K=1.8 -4 a: 0.72

M=viscosity average molecular weight.

The same formula was used to calculate the molecular weights of thestyrene-alpha-olen copolymers, although admittedly this is anapproximation.

The following examples are given to illustrate the invention.

Example I The general procedure used to prepare the copolymers of thisinvention was as follows:

A two-liter resin pot was equipped with a turbine stirrer, athermometer, a dropping funnel, and a charging port containing aself-sealing rubber stopper through which catalyst could be added bymeans of a syringe. The apparatus was baked at about 150 for 18 hourswhile nitrogen was passed through the pot. After the apparatus was thusconditioned, it was cooled under nitrogen and the desired amounts oftitanium trichloride catalyst were added through the charging port.Next, a measured amount of triisobutyl aluminum cocatalyst was added bysyringe through the charging port. The heptane solvent was then addedthrough the dropping funnel. The styrene 4 particles when the stirrerwas stopped. The copolymers were recovered by ltration, washed withmethanol and dried.

To illustrate the method, a series of copolymerizations were run usingstyrene and l-octene mixtures of varying ratios. The amounts ofcatalyst, solvent, and monomers are given in Table I along with thepercent yield of copolymers, the copolymer composition, the intrinsicviscosity of the copolymers, and the percent crystallinity of thecopolymers.

TAB LE I Copolymerization of styrene with 1Octcne Run N o. I-l L2 I-3I-4 1-5 I- I-7 TiCla, 0. 94 1. 07 l. 00 1.05 Iso-BugAl, ml. 2. 2. 70 2.55 2. 65 Heptane, mi.-- 582 521 700 1090 Styrene, ml 423 482 400 267l-octene, ml 47 53 100 157 Yield, percent 43. 1 47. 4 47. 7 42. 7Intrinsic viscosity, [n]u 7. 93 6. 74 6. 45 4. 61 Octene in copolymer,mol

percent b 0 2. 1 3. 3 5. 7 9. 0 15 31 Crystallinity, percent 25 19. 225. 1 18. 3 12. 9 17. 7 10. 9

Intrinsic viscosity measured in chlorobcnzene at 30 C.

b Copolymer analysis by nuclear magnetic resonance.

Crystallinity determined by dierential scanning calorimetry.

It can be seen from the Table I that copolymers containing from 2.1 to31 mole percent of 1-octene have been prepared by varying the amounts ofmonomers, catalyst, and solvent used. The crystallinities of theresulting copolymers may be increased by annealing the samples.

Example II To illustrate the increased rate of molecular weightdegradation of the styrene/ l-octene copolymers over the rate ofdegradation of the polystyrene, the polymer and copolymers prepared inExample I were heated in the presence of air at the temperatures shownand for the times indicated in Table II. The degradation in molecularweight, and the drop in intrinsic viscosity of the samples, is shown inthe Table Il and the initial rate of degradaand comonomer were thenmixed and added to the drop- 40 tion is shown graphically in FIG. I ofthe drawings.

TABLE II Degradation of Styrene/l-Octene Copolymers Initial molecularMole weight Molecular weight b after degradation percent ml Sample No1octene [1;]5 Mv Hours Temp., C. [11] Mv 1, o

I-1 0 4. 15 1, 900, 000 6 150 5. 00 2, 400, 000 1. 2l 24 150 4. 42 2,100, OOO L 06 lnlo=1nitial intrinsic viscosity measured in chlorobenzeneat 30 C. Mv=viscosity average molecular Weight calculated from [1;]0.

b []=Intrinsic viscosity after degradation measured in chlorobenzeue at30 C. Mv=viscosity average molecuiar weight calculated from [q].

ping funnel. All manipulations were performed under a head of nitrogen.The stirrer was then started and allowed to stir at about 1,000 r.p.m.throughout the polymerization. When the resin pot had been heated to 90C., the monomers were added dropwise from the funnel, while controllingthe temperature of the reaction mixture at 90 C.i2 C. After about 6hours, the reaction mass was allowed to cool to about C. and thecatalyst was killed by the addition of 200 ml. of methanol followed bystirring and heating to reux for one hour. The co- Referring to FIG. Iof the drawings, the viscosity of the copolymer after degradation hasbeen divided by the initial viscosity in order to normalize all thecurves to a single starting point. It may be seen from the iigure thatthe initial rate of degradation in molecular weight increases as themole percent of 1octene in the copolymer increases. The increase inviscosity of the polystyrene sample I-l is probably due to a smallamount of crosslnking which occurs prior to degradation. The sample thenstarts to degrade as indicated by the 24 hour heat;

polymers settled out to the bottom of the pot as white ing.

Example III To illustrate the general applicability of the use ofalpha-oleins as an aid to more rapid degradation of molecular weight ofcrystalline polystyrene, a series of copolymers was made by the generalmethod outlined in Example I. The mole percent comonomer in thecopolymers and the initial intrinsic viscosity of the copolymers isrecorded in Table III. Each copolymer was subjected to heat in thepresence of air from l to 24 hours and the resulting intrinsic viscositymeasured. The results are also tabulated in Table III. Molecular weightsare included for convenience.

(b) lowering the molecular weight of said copolymers by heating it inair at a temperature of between 100 C. and 260 C. until the desiredmolecular weight has been obtained, whereby the rate of degradation isincreased over the rate of degradation of crystalline polystyrene whilethe degree of crystallinity of the resulting product is increased overthat of said copolymer.

2. The process of claim 1 wherein said alpha-olefin is selected from thegroup consisting of propylene, 1butene, l-pentene, 3methyllbutene,l-hexene, 1-octene, and ldecene.

TABLE III Degradation oi Styrene/a-Olen copolymers Initial molecularweight Molecular weight b after degradation Sample Comonomer, mole No.and in copolymer [fzln Mv Hours Temp., C. [n] MV ['Ilinla III-1 None, o4. 15 1, 90o, nuo e 15o o 2, 400, 000 1. 21 24 150 4. 42 2, 100, 000 1.06

III-2 Propylene, 5.0 4. 37 2, 000, 000 150 2. 87 1, 150, 000 0. 68 24150 0. 79 190, 000 0. 18 6 200 0. 18 24, 000 0. 041 24 200 0. 08 7, 8000. 018

III-3 3lnethyl1butene, 20.- 8. 65 5, 200, 000 6 150 6. 19 3, 250, 000 0.72 24 150 3. 64 1, 600, 000 0. 42 6 200 0. 28 45, 00 0. 032 24 200 0. 1620, 500 0. O18

III-4 1-pentene, 16.0 8. 59 5, 000, 000 4 150 2. 21 800, 000 0. 26 6150 1. 87 640, 000 0. 22

III-5 1-pentene, 20.0 7.40 4,200,000 2 150 4.50 2, 100,000 0. 61 6 1503. 52 1, 500, 000 0. 48

III-6 1pentel1e, 35.0 6. 82 3, 700, 000 1 150 4. 39 2, 000, 00D 0. 64 3150 0. 77 190, 000 0. 11

III-7 1hexene, 7.0. 5. 1 2, 500, 000 8 150 4. 25 l, 950, 000 0. 83 24150 3. 94 1, 750, 000 0. 77 6 180 0. 61 13 00 0. 12 24 180 0. 25 38, 5000.049

III-8 1-heXel1e, 12.0 4. 78 2, 300, 000 6 150 l. 85 620, 000 0. 39 24150 0. 92 240, 000 0. 19

III-9 l-hexene, 22.0 5. 59 2, 800, 000 6 150 0. 77 190, 000 0. 14 24 1500. 36 65, 000 0. 064

III-10.-- 1-decene, 6.0 7. 47 4, 200, 000 4 150 4. 99 2, 400, 000 0. 67

l [11]=Initial intrinsic viscosity determined in chlorobenzene at 30 C.Mv=viscosity average molecular wel ht calculated from [11] n. b1;]=Intrinsic viscosity after degradation measured in chlorobenzene at30 C.Mv=viscosity average molecular weight calculated from [17].

From the table it is apparent that the use of 180 C. or 200 C. ratherthan 150 C. for the degradation greatly increases the rate of molecularweight decrease. FIG. 2 of the drawings is a normalized plot of relativeinitial rates of degradation at 150 C. There is no apparent correlationbetween number of carbons of the alpha-olen and the rate of degradationof molecular weight.

What is claimed is:

1. A process for preparing a highly crystalline, isotactic polystyreneproduct having a molecular weight of less than 1,000,000 comprising:

(a) preparing a highly crystalline, isotactic copolymer having amolecular weight of greater than 1,000,- 000 and consisting of styreneand from 2 to 20 percent by weight of an alpha-olefin having from 3 to10 carbon atoms; and

UNITED STATES PATENTS 3,157,624 1`1/ 1964 De Vries 26o-88.2 3,414,55312/ 1968 Kern 26o-93.5

JAMES A. SEIDLECK, Primary Examiner R. S. BENJAMIN, Assistant ExaminerU.S. Cl. X.R. 26088.2 S

